grayling either were not entering the pit or were consumed by pike soon 

 after entering. Northern pike were apparently spawning in the pit because 

 many age-0 pike were caught or observed in the shallows throughout the 

 summer. During September, age-0 pike were observed in the river in a large 

 pool opposite the pit outlet, apparently moving from the pit to the river. 

 Thus, the pit may be increasing the number of pike in the river system in 

 general and, given the high density of age-0 and age-l Arctic grayling 

 observed in the river near the pit, may lead to a localized increase in the 

 density of river-dwelling northern pike near the pit. Studies by Alt (1970) 

 and Cheney (1972) indicate that movements of northern pike in the rivers of 

 the nearby Minto Flats region may not be extensive. On a small river, such 

 as the West Fork Tolovana River, a local increase in the northern pike 

 population may lead to local reductions in the Arctic grayling population. 



The upper pit at the Tanana Ri ver-Upstream site had a similar habitat 

 and also provided a spawning, rearing, and feeding area for northern pike as 

 well as a feeding area for least c i sco and humpback whitefish (Figure 57). 

 On a large river, as at the Tanana Ri ver-Upstream pit, the effects of the 

 increased numbers of northern pike must be minimal when compared to the 

 river population. The main effect of a deep pit on this type of river system 

 is providing a clear water feeding area that increases the availability of 

 desirable species to sport fishing. The lower pit was a more uniform depth 

 with minimal littoral area and was used as a spawning and feeding area by 

 I ongnose sucker. The connection between the two pits, a shal low (8 cm deep) 

 stream, was used by longnose sucker fry, lake chub, and juvenile chum salmon 

 as a rearing area. The lower pit was also utilized as a feeding area by 

 humpback whitefish, least cisco, northern pike, and burbot. 



The Tanana River-Downstream pit was a deep (maximum depth = 9.4 m) 

 Clearwater pit with apparently very low productivity. Fish species captured 

 in the pit were longnose sucker, Bering Cisco, and Chinook salmon. There 

 was no connection to the river, thus, the fish apparently immigrated during 

 high water and became trapped after the water level dropped. 



189 



